This invention relates to a method of concentrating grape juice by evaporating one part of its water content.
For the purpose of concentrating grape juice, the latter is, after being pressed from the grapes, admitted to an evaporator in which its water content is removed to a desired extent by evaporation. The evaporator may be a plate-type, spiral or tubular heat exchanger or evaporator in which the grape juice is heated and concentrated to approximately 50.degree.-72.degree. Brix. This process involves the problem of the formation of potassium bitartrate (cream of tartar) deposits which appear increasingly during grape juice concentration. Cream of tartar deposits cause encrustation and clogging in the evaporator, particularly towards the end of the concentration process, necessitating a frequent opening and cleaning of the apparatus which, in turn, results in a reduced efficiency and increased energy consumption.
It has been attempted to remedy the above drawback by reducing the cream of tartar concentration of the grape juice as much as possible prior to the evaporation process. For this purpose, the grape juice is cooled to approximately 0.degree. C. and then stored for about ten days until the cream of tartar crystals are formed and grow to such an extent that they settle or that they may be separated by appropriate filters. In other processes the crystallization is accelerated by the addition of crystals, also performed at a temperature of approximately 0.degree. C.
According to the above processes, the entire juice quantity obtained as a result of the grape pressing step has to be cooled to approximately 0.degree. C. which means a significant refrigeration input. Further, the relatively long standing period of large juice quantities in a cooled state needs a correspondingly large number of vessels thus requiring a significant machinery input.
It has further been attempted to counteract deposits and clogging particularly in multi-stage evaporators by switching the high-concentrate stage to a previous stage of the evaporator. In this manner, clogging of the evaporator apparatus may be slightly delayed. The required maintenance (cleaning) work has to be performed as before.
In all above-mentioned cream of tartar stabilizing methods which originate in wine making, the concentration of cream of tartar may be lowered to approximately 2 g/l at the most, which corresponds to a saturation degree of the natural grape juice at approximately 0.degree. C. This quantity, however, is still sufficient to cause deposits and clogging in the evaporator, particularly in case of a desired juice concentration of 45.degree.-72.degree. Brix.
The above-discussed problem applies equally to the cooling of the juice concentrate after the completion of the evaporating process, in which case the concentrate refrigerator through which the juice concentrate passes is also exposed to clogging by cream of tartar and, accordingly, has to be frequently cleaned.